Field of the Invention
The present invention relates to variants of GH Family 11 xylanases, polynucleotides encoding the variants, methods of producing the variants, and methods of using the variants.
Description of the Related Art
Xylan, a major component of plant hemicellulose, is a polymer of D-xylose linked by beta-1,4-xylosidic bonds. Xylan can be degraded to xylose and xylo-oligomers by acid or enzymatic hydrolysis. Enzymatic hydrolysis of xylan produces free sugars without the by-products formed with acid (e.g., furans).
Xylanases can be used in various applications such as enzymatic breakdown of agricultural wastes for production of alcoholic fuels, enzymatic treatment of animal feeds to release free sugars, enzymatic treatment for dissolving pulp in the preparation of cellulose, and enzymatic treatment in biobleaching of pulp. In particular, xylanase is useful in the paper and pulp industry to enhance the brightness of bleached pulp, improve the quality of pulp, decrease the amount of chlorine used in the chemical pulp bleaching steps, and to increase the freeness of pulp in recycled paper processes.
Dumon et al., 2008, Journal of Biological Chemistry 283: 22557-22564, describe the engineering of hyperthermostability into a GH11 xylanase. Wang and Tao, 2008, Biotechnology Letters 30: 937-944, disclose the enhancement of the activity and alkaline pH stability of Thermobifida fusca xylanase A by directed evolution.
U.S. Pat. Nos. 5,759,840, 7,510,860, and 7,695,947 disclose modifications of Family 11 xylanases to improve thermophilicity, alkalophilicity and thermostability. U.S. Pat. No. 7,060,482 discloses modified xylanases comprising either a basic amino acid at position 162 corresponding to the Trichoderma reesei xylanase (TrX) amino acid sequence, or its equivalent position in other xylanase molecules, at least one disulfide bridge, or a combination thereof. U.S. Pat. No. 7,314,743 discloses a modified xylanase having at least one substituted amino acid residue at a position corresponding to the Trichoderma reesei xylanase II amino acid sequence. WO 2007/115391 discloses a modified Family 11 xylanase enzyme comprising cysteine residues at positions 99 and 118 corresponding to the Trichoderma reesei xylanase II amino acid sequence to form an intramolecular disulfide bond.
The present invention provides variants of a xylanase with improved properties compared to its parent enzyme.